The overall objectives of the project concern learning more about the regulation of gene expression in differentiating cells in developing embryos and also about the nucleotide sequence organization of the eucaryotic genome. We are particularly interested in sequences in and adjacent to transcription regions and replication initiation regions in nuclear DNA. These studies are primarily being conducted in sea urchin embryos. In native DNA from embryos, we are studying naturally occurring regularily spaced single-stranded regions. We are also characterizing the length and position of repeating long polypyrimidine stretches in embryo DNA. Our further work also concerns methylation in vivo of palindromic and repetitive sequences in nuclear DNA from different stages of embryogenesis. BIBLIOGRAPHIC REFERENCES: Case, S.T. and R.F. Baker, Investigation into the use of Aspergillus oryzae S1 nuclease in the presense of solvents which destabilize or prevent DNA secondary structure: formaldehyde, formamide, and glyoxal. Analytical Biochemistry 64, 477-484 (1975). Case, S.T., C.A. Talkington and R.F. Baker, The effect of 5-bromodeoxyuridine on the synthesis of nuclear and cytoplasmic DNA-binding proteins isolated from sea urchin embryos. Cell Differentiation 4, 55-62 (1975).